1. Technical Field
The present invention relates to a filter device for gas that is used while being connected to a fuel flow path on the intake side of a gas engine operating with gas fuel such as liquefied petroleum gas (LPG) and compressed natural gas (CNG), for example.
2. Related Art
Conventionally, in a gas engine that uses gas fuel such as LPG and CNG, it is known that fuel residue of impurities in oil form caused by tar contained in gas fuel in mist form, plasticizer eluted from a hose, or the like (referred to as “fuel residue”, hereinafter) flows into an injector on the downstream side, resulting in adverse effect on the injector function.
Therefore, as a means of preventing such fuel residue being mixed into an engine, a means of preventing the fuel residue being mixed into an injector or an engine is by providing a filter device for gas in the middle of the fuel flow path.
For example, there is a known filter device for gas disclosed in Japanese Laid-Open Patent Publication No. 7-328364 that includes: a cylindrical filter case; a hollow filter that is also cylindrical and provided inside the filter case; and an inlet and an outlet on the top part of the filter case. The filter device for gas is configured in such a manner that gas flowing in from the inlet passes the inside of the filter case, passes through the hollow filter, flows into a space outside of the hollow filter, and then is discharged to the outlet.
In addition, there is a known filter device for gas disclosed in Japanese Laid-Open Patent Publication No. 2011-245442 configured in such a manner that gas flowing into a filter case from an inlet is filtered by a hollow filter provided in the filter case, and the gas that has passed inside the hollow filter is discharged through an outlet.
As described above, a way that gas flows from an inlet to an outlet in the conventional filter devices for gas can roughly fall into a type where gas passes from the inside of the cylindrical hollow filter to the outside thereof, and a type where gas flowing into the filter case flows from the outside of the hollow filter into the inside thereof through the filter and is discharged.
In Japanese Laid-Open Patent Publication No. 2011-245442 disclosing a filter device for gas of the latter type, there is a known filter device for gas capable of efficiently trapping gas flowing inside the filter case on the hollow filter by providing a flow controlling plate that controls a flow of gas flowing into the inlet as a filter device for gas that extends life of the hollow filter by efficiently contacting gas flowing into the filter case to the hollow filter, and by separating impurities.
This filter device for gas is designed in such a manner that gas that has passed through the hollow filter flows to the outlet positioned on one end of the hollow filter in the axial direction. In addition, the outlet has substantially the same inner diameter with the hollow filter, and the flow path is a straight line. Therefore, it is thought that there is no obstacle that distributes flow speed distribution and thus any problem of non-uniformity of the flow speed distribution on the outlet side or the like is not caused.
On the other hand, in a case of a filter device for gas where gas flows in the former way, an outlet 24 is formed to be eccentric as illustrated in FIG. 3. Therefore, non-uniformity occurs in the flow speed distribution of gas at a filter outer peripheral section 35 of a hollow filter 3 or around the outlet 24 (resulting in decrease of trap effect at a part having a high flow speed on the hollow filter 3), and thus liquid of fuel residue or the like attached to an inner peripheral wall 21 of the filter case is discharged to the outlet 24 together with gas at a part having a high flow speed of gas on the inner peripheral wall 21 of the filter case, which is around the outlet 24. Consequently, a failure of an engine system is caused.
In order to solve this problem, there is a known method of providing a communication hole to narrow a flow path, the hole being positioned short of a point connected to an outlet as disclosed in Japanese Laid-Open Patent Publication No. 7-328364, and there is also a known method of providing a space of a predetermined length between a hollow filter and an outlet so as to decrease flow speed and thus decrease an influence of non-uniformity of flow speed distribution as disclosed in Japanese Laid-Open Patent Publication No. 2009-114996.